The formation of high quality thin silicon (Si) films constitute an integral part of micro-circuit manufacture. Thin Si films are used to form gate structures of thin film transistors, the cell dielectric of dynamic random access memory (DRAM), and other conductive and non-conductive micro-structures.
The most effective, but also the most expensive and slowest method for depositing very thin defect-free films is molecular beam apitaxy (MBE), wherein layer-by-layer growth is accomplished under ultra-high vacuum.
Thin Si films are most commonly, and most inexpensively formed by CVD through the reaction of hydrogen with silicon tetrachloride (SiCl.sub.4), or through the deposition of silane (SiH.sub.4) followed by a pyrolitic decomposition into Si and H.sub.2.
The thinness of reliable film achievable through such a process is limited by the defect density (pinholes) and deformity resulting from the uneven formation, inherent to the CVD process, of scattered islands at low energy sites on the substrate, followed by a growth and merging of these islands into a continuous layer.
This invention results from efforts to improve the quality of CVD thin films. It is based on previous observations that, compared to silane, higher order silicon hydrides (Si.sub.n H.sub.2n+2 where n&gt;1) or polysilanes exhibit several orders of magnitude higher sticking probabilities on Si than silane, and lower decomposition temperatures; and that disilane (Si.sub.2 H.sub.6) adsorption at room temperature occurs at random distribution of sites which are not correlated with defects of steps (Stephen M. Gates, Adsorption Kinetics of SiH4 . . . on the Si(111)-(7X7) Surface, Surface Science v.195, p.307-329 (1988); S. M. Gates et al. Decomposition of Silane and Si surfaces below 500.degree. C. J. Chem. Phys 92(5) p.3144-3152 (1 Mar. 1990); R. Tsu et al. Adsorption and Dissociation of Si.sub.2 H.sub.6 on Ge, Surface Science v.280, p.265-276, (1993)).